This invention relates to apparatus for metering particulate material and particularly to a roller metering device of a type which includes a plurality of longitudinal grooves around the roller which grasp and carry the particulate material, and to a cleaning device for cleaning the grooves.
Roller metering arrangements have become used widely in devices for metering and spreading particulate material such as fertilizer, herbicides and the like. In arrangements of this type it is common for the roller to be positioned at the bottom of a hopper so that the roller feeds forwardly from the hopper a metered curtain of the material, the curtain falling into separate cups positioned along the length of the roller from which the material is pneumatically distributed to spreaders separated along the length of a boom. These devices have successfully operated on widely different materials and at widely varying distribution rates.
The metering roller, in order to achieve the most accurate metering, preferably includes a plurality of continuous grooves longitudinally along its length. With such continuous grooves, the material is accurately grasped and carried by the volume of the groove so that the metering rate is substantially constant regardless of changes in orientation of the roller caused by movement of the machine across uneven terrain or other variables.
While such rollers with continuous elongate grooves have been found to be most effective for accurate feeding, they have to date had a serious problem which has not been overcome until the development of the present invention. Specifically, when the particulate material to be metered contains any moisture or has any other adhesive properties, it tends to stick to the roller and hence gradually clogs the grooves and changes their dimensions thus interfering with the proper and accurate metering of the material. To date therefore this problem has effectively prevented the use of rollers of this type with the metering of particulate material which has such tendency to stick to the rollers.
Recent developments in the addition of liquid chemicals, for example herbicides, to particulate materials, for example fertilizer, have significantly increased the desirability for a device which can handle such particulate materials which are moist or have other adhesive properties.
It is appreciated that a single pass of equipment which spreads both the liquid chemical and the particulate material is much to be preferred.
Attempts have been made to solve the problems of cleaning action upon a roller metering system. In a first attempt, one example of which is illustrated in U.S. Pat. No. 4,053,088 (Nodet Gougis), the grooves in the roller are not continuous but are broken into separate pieces as defined by projecting fingers which extend outwardly from the roller and which engage and forward the particulate material. In between the fingers, a cleaning blade is presented which acts to scrape the roller on a constant diameter of the roller so that the fingers themselves are not cleaned. This technique tends to cause effective cleaning of the roller but unfortunately the discontinuous feeding mechanism defined by the individual fingers allows material to slip by the roller rather than to be positively fed by the roller and thus seriously reduces the accuracy of the feeding system.
Alternative techniques for attempting to clean the roller have used brushes which merely rotate about an axis parallel to the roller and include bristles which flex on each attempt to enter into the recesses defined by the grooves so the bristles flick in and out of the grooves and act to clean the grooves. In theory this technique is an effective technique in that it provides the continuous grooves required for accurate metering but in practice the constant flexing of the bristles necessary to move over the roller surface and to extend into the recesses causes the bristles to rapidly break down. This device has therefore received little commercial success.